In describing the embodiments of the invention, specific terminology is chosen for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.
Several agrochemical active ingredients used for long periods of time are often used at high dosages for countering pests and diseases, which is a constant burden on the environment. Active ingredients which have a low solubility in water and are highly soluble in water-immiscible solvents are typically formulated as emulsifiable concentrates, microemulsions or capsulated suspensions.
Emulsifiable concentrates often perform very well, are stable, and offer good efficacy but pose a severe risk and threat to the environment in terms of toxicity.
Microcapsules or capsulated suspensions which encapsulate the active ingredient within a polymeric wall offer particular advantages. The encapsulation of the pesticidal active ingredients makes the formulation safe for the applicator or the end user. Since the pesticide is enclosed in a polymeric shell wall, the user is not directly exposed to the chemical. The use of an encapsulated composition ensures activity of the active ingredient over an extended period of time, since the active ingredient is released continuously into the environment rather than in one single dose. Microencapsulated pesticides of the controlled release or the quick release types, are usually sold in the form of aqueous suspensions of the microcapsules. However, microcapsules or capsulated suspensions are found to be unstable over broad temperature ranges. Besides, they exhibit a high tendency of crystallization of the active ingredients. Further, capsulated suspensions suffer from disadvantages of higher packaging costs.
Due to these drawbacks, it is advantageous to provide such microencapsulated compositions in a dry form, such as water dispersible granules rather than as aqueous suspensions. Dry formulations can be prepared with a relatively high loading of the pesticide, are easier to remove from the containers and produce less contamination in the environment. Furthermore, dry formulations are preferred as they can be stored over longer periods of time and do not require the simultaneous storage and transport of large volumes of water.
Dry forms such as water dispersible granules are particularly preferred as they can be stored for over longer durations, over wide extremes of temperature, without destroying the stability of the formulation. In addition, it is convenient to provide a solid formulation of microencapsulated pesticides, which is water dispersible and can be readily mixed with water to produce sprayable materials. Further, shipping costs are reduced since inclusion of solvents, water carriers and water-based flowable pesticide formulations is eliminated.
Water dispersible granules of microcapsules within polyurea shell wall are known. U.S. Pat. No. 6,419,942 discloses water dispersible granule composition of microcapsules encapsulating an active ingredient. It is observed that these prior art granules are difficult to dry and choke the nozzle. It is observed that the formulation forms lumps in the spray suspension, when the formulation is diluted in water. Also, these granules demonstrate average biological efficacy and poor suspensibility, particularly upon accelerated storage. U.S. Pat. No. 6,919,942 is also silent on the physical properties of the formulation.
It is understood that a composition may demonstrate satisfactory initial dispersibility but may not necessarily demonstrate good suspensibility. Thus, it is always desirable to have a water dispersible granule formulation that not only disperses spontaneously, but also remains suspended upon dilution for a continuous period of time. There is a further need to develop a water dispersible granule formulation of microcapsules which is effective for an extended period of time, with reduced dosage of application.